Re: Will bad milk ruin all future kefir batches?

I heard that bad bacteria is always there, it's just a matter of good/bad ratio.

I rinse mine before each batch, to ensure that. Even more when I use the milk I stored the kefir with, when just a few days, for the next batch, and that makes it extra thick. It might be normal sour milk (or whatever the milk is called when it thickens outside the fridge.

Let us know if you found a good scientific answer! (I'd like parameters of temperature, taste, consistency… so I can tell when it's good or bad)